1. Field of the Invention
The present invention generally relates to audio speed conversion, and more particularly, to a method and system that enables audio speed conversion such as voice speed conversion.
2. Background Information
Speed conversion systems can be used to enable multiple speed operation (e.g., fast, slow, etc.) in video and/or audio reproduction systems, such as color television (CTV) systems, video tape recorders (VTRs), digital video/versatile disk (DVD) systems, compact disk (CD) players, hearing aids, telephone answering machines and the like. Conventional audio speed converters generally differentiate between a silence interval and a sound interval in an audio signal. Deleting the silence interval and compressing the sound interval results in an increased audio speed. Conversely, expanding the silence and sound intervals results in a decreased audio speed. Many conventional audio speed converters increase or decrease audio speed at a constant rate independent of the contents. Accordingly, these types of audio speed converters can not take full advantage of the silence and redundant intervals of an audio signal.
The process of removing or repeating intervals of an audio signal can be problematic since it often produces undesirable audible “clicks.” Additionally, the pitch of an audio signal should not be changed or transformed to other frequencies since the human ear tends to be quite sensitive to these changes. Known prior art algorithms such as the “pointer interval control overlap and add” (PICOLA) algorithm address these problems by multiplying an audio signal by a window function in an attempt to smooth the output signal and maintain the original pitch. This results in producing synthetic waveforms that were not part of the original audio signal. Moreover, the use of such algorithms typically requires utilization of fast digital signal processors (DSPs), which tend to be expensive. Accordingly, it is desirable to provide an audio speed converter which avoids the use of expensive digital signal processors (DSPs), and utilizes more cost-effective processing means such as small programmable logic devices (PLDs). The present invention addresses these and other problems.